More advanced preparation method of organic-transition metal hydride complexes containing aryl group or alkyl group as hydrogen storage materials

ABSTRACT

The present invention relates to a more advanced preparation method of organic-transition metal hydride as a hydrogen storage material, precisely a more advanced preparation method of organic-transition metal hydride containing aryl or alkyl group that facilitates safe and reverse storage of massive amount of hydrogen. The present invention relates to a preparation method of an organic-transition metal hydride comprising the steps of preparing a complex reducing agent composition by reacting alkali metal, alkali earth metal or a mixture thereof and (C10-C20) aromatic compound in aprotic polar solvent and preparing organic-transition metal hydride by reacting the prepared complex reducing agent composition and organic transition metal halide. The method of the present invention has advantages of minimizing the numbers and the amounts of byproducts by using a complex reducing agent and producing organic-transition metal hydride safely without denaturation under more moderate reaction conditions.

This application is a Divisional of U.S. Ser. No. 12/538,209 filed onAug. 10, 2009, which claims priority of Korean application no10-2008-0078334 filed on Aug. 11, 2008.

TECHNICAL FIELD

The present invention relates to a preparation method oforganic-transition metal hydride as a hydrogen storage material, whereinthe organic-transition metal hydride absorbs hydrogen to store it.

BACKGROUND ART

Many research groups proposed different hydrogen storage materials suchas metal hydrides, chemical hydrides (NaBH₄, KBH₄, LiBH₄, etc),metal-organic framework (MOF), nano-structure materials (CNT, GNF, etc),polymer-metal complex compounds, etc. However, these proposed hydrogenstorage materials have disadvantages for commercialization as storagematerials, for example; 1) poor hydrogen storage capacity that cannoteven reach the minimum hydrogen storage rate (6 wt. %) proposed by USDOE (department of energy) for practical use; 2) poor reproducibility ofhydrogen storage capacity; 3) requiring tough conditions for hydrogenabsorption and desorption; 4) structural disintegration during hydrogenabsorption and desorption; and 5) requiring the development ofreproduction process.

In the case of the organic-transition metal hydride recently developedand applied for patent by Hanwha Chemical Cooperation R&D Center, itseems to be adequate for commercialization owing to the advancedproperties such as 1) improved hydrogen storage capacity with highefficiency, compared with the conventional hydrogen storage materialbecause of Kubas binding between hydrogen and a specific transitionmetal (Ti, Sc, V, etc); 2) moderate conditions for hydrogen absorptionand desorption (absorption: 25° C., 30 atmospheric pressure; desorption:100° C., 2 atmospheric pressure); and 3) no-structural disintegrationduring hydrogen absorption and desorption (Korean Patent ApplicationNumbers 10-2007-0090753, 10-2007-0090755, and 10-2008-0020467).

Korean Patent Application No 10-2007-0090753 and Korean PatentApplication No 10-2007-0020467 describe methods for preparingorganic-transition metal hydride based on hydrodehalogenation (-M-Xbond→-M-H bond) using a hydrogen source and a catalyst. However, thesemethods cannot avoid the problem caused by catalytic poisoning andside-reaction by inorganic hydroxide used as a neutralizing agent.Besides, separation and purification of a produce is not easy andvarious byproducts are produced by solvent.

To overcome the said problems, Korean Patent Application No10-2008-0020467 provides a method to produce organic-transition metalaluminum hydride complex by reacting organic transition metal halide andaluminum hydride compound and then to produce organic-transition metalhydride by reacting the produced organic-transition metal-aluminumhydride complex with Lewis base.

However, the Korean Patent Application No 10-2008-0020467 has thefollowing problems.

First, in relation to the reaction step, a target product is produced by2-step reaction. Thus, this reaction exhibits lower efficiency and takeslonger time, compared with 1-step reaction.

Second, in relation to the process of separation and purification of theintermediate (organic-transition metal-aluminum hydride complex)produced from the first reaction step, alcohols used for separation andpurification of the intermediate are reacted with the intermediate toproduce diverse byproducts.

Third, in relation to the separation and purification of the finalproduct produced from the second reaction step, triethyl amine and butyllithium used as Lewis base are very well dissolved in a polar ornon-polar solvent, so that it is very difficult to separate thesecompounds from the product completely when they are present asnon-reactants.

Therefore, the Korean Patent Application No 10-2008-0020467 is limitedin production of organic-transition metal hydride with high yieldbecause of the said problems.

DISCLOSURE Technical Problem

It is an object of the present invention to provide a preparation methodof organic-transition metal hydride which facilitates hydrogen storagewith high capacity. high efficiency but overcomes the difficulties inseparation and purification of a product.

It is also an object of the present invention to provide a preparationmethod of organic-transition metal hydride that can be used as ahydrogen storage material for operating small to medium size fuel cellsbecause of comparatively moderate conditions required for hydrogenabsorption and desorption, compared with the conventional hydrogenstorage materials.

Technical Solution

To overcome the said problems, the present invention provides apreparation method of organic-transition metal hydride in which acomplex reducing agent having strong reducing power is used for reactionand the numbers and the amounts of byproducts are minimized undercomparatively moderate reaction conditions.

More precisely, the method of the present invention comprises thefollowing steps:

a) preparing a complex reducing agent composition by reacting alkalimetal, alkali earth metal or a mixture thereof with(C10-C20) aromaticcompound in aprotic polar solvent; and

b) preparing organic-transition metal hydride by reacting the preparedcomplex reducing agent composition and organic-transition metal halide.

In step a), the alkali metal, alkali earth metal or the mixture thereofprovides electrons in the presence of aprotic polar solvent and thearomatic ring compound receives the electrons, resulting in thepreparation of an activated complex reducing agent composition.

In step b), the activated complex reducing agent composition inducesdehalogenation of the organic-transition metal halide and the aproticpolar solvent provides hydrogen, resulting in the preparation oforganic-transition metal hydride.

In step b), the reaction temperature is −80-50° C., preferably −50-30°C., and more preferably −30-25° C. If the reaction temperature is lowerthan −80° C., the reaction cannot be finished. If the reactiontemperature is higher than 50° C., the produced organic-transition metalhydride might be decomposed.

In step b), the reaction time is 1-72 hours, preferably 1-48 hours, andmore preferably 1-24 hours. If the reaction time is less than one hour,the reaction cannot be finished, and if the reaction time is longer than72 hours, the produced organic-transition metal hydride might bedecomposed.

After step b), the produced organic-transition metal hydride can beseparated by using one or more non-polar solvents selected from thegroup consisting of pentane, toluene, benzene, ether and theirderivatives.

The non-polar solvent can be one or more compounds selected from thegroup consisting of pentane, toluene, benzene and their derivatives.When a polar solvent containing alcohol is used, there might be sidereaction of organic-transition metal hydride and the organic-transitionmetal hydride and the byproduct are dissolved in the solvent, whichmakes the separation and purification of organic-transition metalhydride difficult.

The alkali metal or alkali earth metal is strong electron-donor metal,which is exemplified by Li, Na, K, Rd, Cs, Fr, Mg, Ca, Sr, Ba and Rd.Among these, alkali metal having stronger reducing power is preferredand Li in the form of small granules is more preferred.

In the present invention, the aromatic ring compound is the electronrecipient and contains at least two benzene rings or fused with twobenzene rings, which can be selected from the group consisting ofnaphthalene, biphenyl, phenanthrene, anthracene, trans-stilbene andtheir derivatives. But, naphthalene and its derivatives are morepreferred because they are easy to handle and have excellent sublimationproperty and are easy to eliminate after the reaction.

The molar ratio (A:B) of transition metal (A) of organic-transitionmetal halide to alkali metal or alkali earth metal or a mixture thereofand aromatic ring compound (B) is preferably 1:0.0001-1:10. In thisrange, production of byproducts can be reduced.

The aprotic polar solvent is the source of hydrogen and at the same timeacts as a solvent, which can be selected from the group consisting oftetrahydrofuran (THF), 1,2-dimethoxyethane (DME), dioxane (DXN),diethylene glycol dimethyl ether (Diglyme), dimethyl formamide (DMF),dimethylsulfoxide (DMSO), dimethylacetamide (DMA), hexamethylphosphoramide (HMPA) and their derivatives. Preferably, the aproticpolar solvent can be selected from the group consisting oftetrahydrofuran (THF), 1,2-dimethoxyethane (DME), dioxane (DXN),diethylene glycol dimethyl ether (Diglyme), dimethyl formamide (DMF) andtheir derivatives. It is more preferred to select one or more compoundsamong tetrahydrofuran (THF), 1,2-dimethoxyethane (DME) and theirderivatives because they have lower boiling points favoring theapplication of Schlenk technology.

In this invention, reaction of each step is preferably performed basedon Schlenk technology under one or more gases selected from the groupconsisting of Ar, N and He and in a glove box considering instability ofthe product.

In this invention, the organic-transition metal hydride is representedby formula 1 and the organic-transition metal halide is represented byformula 2.B¹-(AM¹H_(m))_(n)  Formula 1B¹-(AM¹X_(m))_(n)  Formula 2

In formula 1, B¹ is straight or branched (C2-C20) alkyl, (C6-C20) aryl,(C3-C20) hetero aryl or (C6-C20) ar (C2-C20) alkyl, and the alkyl cancontain unsaturated bond in its carbon chain. Carbon atom composing arylor aralkyl in B¹ can be substituted with hetero atom selected from thegroup consisting of N, O₂, and S.

B¹ can be replaced with one or more substituents selected from the groupconsisting of —NO₂, —NO, —NH₂, —R¹, —OR², —(CO)R³, —SO₂NH₂, SO₂X¹,—SO₂Na, —(CH₂)_(k)SH and —CN, and in that case, R¹-R³ of the substituentcan be selected from the group consisting of straight or branched(C1-C30) alkyls or (C6-C20) aryls, respectively.

A herein is O or S, X¹ is a halogen element, and k is an integer of0-10. M¹ is one or more elements selected from the group consisting oftransition metal elements having the valence of at least 2, moreprecisely, one or more elements selected from the group consisting ofTi, V and Sc. m is an integer that a valence of M¹ −1, more precisely aninteger of 1-6 and more preferably an integer of 2-4. n is an integer of1-10 and more preferably an integer of 2-6.

In formula 2, X is a halogen element selected from the group consistingof F, Cl, Br and I.

More precisely, B¹ of formula 1 can be selected among those compoundsrepresented by the following structures.

The present invention also provides a preparation method oforganic-transition metal hydride, in which the organic-transition metalhydride is selected from those compounds represented by the followingformula 3 and the organic-transition metal halide is selected from thosecompounds represented by the following formula 4.B²-(M²H_(a))_(b)  Formula 3B²-(M²X_(a))_(b)  Formula 4

In formula 3 and formula 4, B² is selected from the group consisting offused ring compounds containing cyclopentadiene derivatives orcyclopentadiene. B² can be replaced with one or more substituentsselected from the group consisting of —NO₂, —NO, —NH₂, —R¹, —OR²,—(CO)R3, —SO₂NH₂, SO₂X¹, —SO₂Na, —(CH₂)_(k)SH and —CN, and in that case,R¹-R³ of the substituent can be selected from the group consisting ofstraight or branched (C1-C30) alkyls or (C6-C20) aryls, respectively.

X¹ is a halogen element, and k is an integer of 0-10. M² is one or moreelements selected from the group consisting of transition metal elementshaving the valence of at least 2, more precisely, one or more elementsselected from the group consisting of Ti, V and Sc. a is an integer thata valence of M²−1, precisely an integer of 1-6 and more preferably aninteger of 2-4. b is limited to the number of rings of the fused ringcompound containing cyclopentadiene derivatives or cyclopentadiene,which is an integer of 1˜10 and more preferably an integer of 2-6.

In B², the fused ring compound containing cyclopentadiene derivatives orcyclopentadiene is selected from the group consisting ofcyclopentadienyl, methylcyclopentadienyl, dimethylcyclopentadienyl,tetramethylcyclopentadienyl, pentamethylcyclopentadienyl,butylcyclopentadienyl, sec-butylcyclopentadienyl,tert-butylmethylcyclopentadienyl, trimethylsilylcyclopentadienyl,indenyl, methylindenyl, dimethylindenyl, ethylindenyl, isopropylindenyl,fluorenyl, methylfluorenyl, dimethylfluorenyl, ethylfluorenyl andisopropylfluorenyl.

Advantageous Effect

The preparation method of the present invention uses a complex reducingagent having strong reducing power, so that it can overcome the problemsof separation and purification of organic-transition metal hydride andgives the product stably with high yield without denaturation.

The preparation method of the present invention can minimize the numbersand the amounts of various byproducts produced from the reaction. Andthe organic-transition metal hydride produced by the method can be usedas a hydrogen storage material for operating small to medium size fuelcells because of comparatively moderate conditions required for hydrogenabsorption and desorption, compared with the conventional hydrogenstorage materials.

BEST MODE

Hereinafter, the preparation method of organic-transition metal hydrideis described in detail with examples. In these examples, phenoxytitaniumtrichloride and cyclopentadienyltitanium trichloride were selected asthe reactant organic-transition metal halide because 1) they are easy tohandle at room temperature; 2) when they are used, the productorganic-transition metal hydride has a low molecular weight but hascomparatively large hydrogen storage capacity; and 3) they are easilyseparated and purified owing to high solubility in non-polar solvent.

Practical and presently preferred embodiments of the present inventionare illustrative as shown in the following Examples.

However, it will be appreciated that those skilled in the art, onconsideration of this disclosure, may make modifications andimprovements within the spirit and scope of the present invention.

EXAMPLE 1 Preparation of Phenoxytitanium Trihydride <1-1>Preparation of1,2-Dimethoxyethane (DME) Complex Reducing Agent

A complex reducing agent was prepared by reacting lithium (0.034 g/4.86mmol) and naphthalene (0.622/4.86 mmol) in 70 ml of 1,2-dimethoxyethaneunder Ar flow in a 250 ml 1-neck round flask for 10 hours.

<1-2>Preparation of Phenoxytitanium Trihydride

Phenoxytitanium trichloride (0.4 g/1.62 mmol) was dissolved in 30 ml of1,2-dimethoxyethane(DME) under Ar flow in a 100 ml 2-neck round flask(reactant 1).

The prepared lithium/naphthalene/1,2-dimethoxyethane(DME) complexreducing agent was slowly dropped in the reactant 1, followed by refluxat 10° C. for 18 hours and then the reaction was terminated.

The reaction solvent 1,2-dimethoxyethane was eliminated by Schlenkmethod under Ar and then the reaction product phenoxytitanium trihydridewas separated.

The solvent was eliminated by Schlenk method to give phenoxytitaniumtrihydride with the yield of 99%.

Yield: 99% ¹H-NMR (CD₃CN-d₃) γ(ppm): 7.28(d, 1H), 6.95(t, 2H), 6.85(t,2H), 7.62 (s, 3H) ESI-MS (positive mode), m/z(relative intensity):[C₆H₅—O—Ti—H₃]+144(9.9), 145(9.4), 146(100), 147(23), 148(10.1) Anal.Calc. for C₆H₅OTiH₃: C, 50.0; H, 5.6. Found: C, 49.5; H, 5.4%.

To identify byproducts and products generated in Example 1, ³⁵Cl-NMR,XRD, IC, EDX, ESR, and XRF were performed. From the results of XRD and³⁵Cl-NMR, it was confirmed that LiCl was produced as a byproduct.Separation and purification was performed by using benzene. As a result,a small amount of LiCl or non reactant was included in the product, eventhough the amount was too small to be detected by XRD and ³⁵Cl-NMR.

To confirm whether LiCl and non reactant were actually included in thereaction product, IC and EDX were performed. As a result, it wasconfirmed that LiCl was included approximately 0.5% in the product.

From the separation and purification test, it was confirmed that LiClwas hardly detected in the product. And benzene was preferred as thesolvent for separation and purification. ESR analysis was also performedwith the product. As a result, oxidation number of Ti was +4. From theresult of XRF assay, it was confirmed that the weight content of Ti was33.2 wt % (theoretical value=33.27 wt %), indicating that high purityproduct was obtained.

EXAMPLE 2 Preparation of Cyclopentadienyltitanium Trihydride<2-1>Preparation of Sodium/Naphthalene/Tetrahydrofuran (Thf) ComplexReducing Agent

A complex reducing agent was prepared by reacting sodium (0.034 g/4.86mmol) and naphthalene (0.622/4.86 mmol) in 70 ml of tetrahydrofuranunder Ar flow in a 250 ml 1-neck round flask for 10 hours.

<2-2>Preparation of Cyclopentadienyltitanium Trihydride

cyclopentadienyltitanium trichloride (0.355 g/1.62 mmol) was dissolvedin 30 ml of tetrahydrofuran (THF) under Ar flow in a 100 ml 2-neck roundflask (reactant 1).

The prepared sodium/naphthalene/tetrahydrofuran (THF) complex reducingagent was slowly dropped in the reactant 1, followed by reflux at 10° C.for 18 hours and then the reaction was terminated.

The reaction solvent tetrahydrofuran was eliminated by Schlenk methodunder Ar and then the reaction product cyclopentadienyltitaniumtrihydride was separated by using toluene.

The solvent was eliminated by Schlenk method to givecyclopentadienyltitanium trihydride with the yield of 98%.

Yield: 98% ¹H-NMR (benzene-d₆) γ(ppm): 5.995(t, 5H), 10.62 (s, 3H)ESI-MS (positive mode), m/z(relative intensity): [C₅H₅—Ti—H₃]+114(9.9),115(9.4), 116(100), 117(23), 118(10.1) Anal. Calc. for C₅H₅TiH₃: C,51.8; H, 6.9. Found: C, 50.5; H, 6.1%.

To identify byproducts and products generated in Example 2, ³⁵Cl-NMR,XRD, IC, EDX, ESR, and XRF were performed and the results are asfollows. From the results of XRD and ³⁵Cl-NMR, it was confirmed thatNaCl was produced as a byproduct. Separation and purification wasperformed by using toluene. As a result, a small amount of NaCl or nonreactant was included in the product, even though the amount was toosmall to be detected by XRD and ³⁵Cl-NMR.

To confirm whether NaCl and non reactant were actually included in thereaction product, IC and EDX were performed. As a result, it wasconfirmed that NaCl was included approximately 0.9% in the product.

From the separation and purification test, it was confirmed that NaClwas hardly detected in the product. And toluene was preferred as thesolvent for separation and purification.

ESR analysis was also performed with the product. As a result, oxidationnumber of Ti was +4. From the result of XRF assay, it was confirmed thatthe weight content of Ti was 40.3 wt % (theoretical value=41.3 wt %),indicating that high purity product was obtained.

The present application contains subject matter related to Korean PatentApplication No. 10-2008-0078334 filed in the Korean IntellectualProperty Office on Aug. 11, 2008, the entire contents of which areincorporated herein by reference.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

The invention claimed is:
 1. A preparation method of organic-transitionmetal hydride comprising the following steps: a) preparing a complexreducing agent composition by reacting alkali metal, alkali earth metalor a mixture thereof with (C10-C20) aromatic compound in aprotic polarsolvent; and b) preparing organic-transition metal hydride by reactingthe prepared complex reducing agent composition and organic-transitionmetal halide; wherein the organic-transition metal hydride is selectedfrom those compounds represented by formula 3 and the organic transitionmetal halide is selected from those compounds represented by formula 4B²-(M²H_(a))_(b)  Formula 3B²-(M²X_(a))_(b)  Formula 4 (In formula 3 and formula 4, B² should beselected from the group consisting of cyclopentadiene, cyclopentadienederivatives, and fused ring compounds containing cyclopentadiene orcyclopentadiene derivatives, B² can be replaced with one or moresubstituents selected from the group consisting of —NO₂, —NO, —NH₂, —R¹,—OR², —(CO)R³, —SO₂NH₂, SO₂X¹, —SO₂Na, —(CH₂)_(k)SH and —CN, and in thatcase, R¹-R³ of the substituent can be selected from the group consistingof straight or branched (C1-C30) alkyls and (C6-C20) aryls,respectively; X¹ is a halogen element, and k is an integer of 0-10, M²is one or more transition metal elements having the valence of at least2, a is an integer that a valence of M²−1, and b is an integer of 1-10).2. The preparation method of organic-transition metal hydride accordingto claim 1, wherein the fused ring compound containing cyclopentadienederivatives or cyclopentadiene in the B² is selected from the groupconsisting of cyclopentadienyl, methylcyclopentadienyl,dimethylcyclopentadienyl, tetramethylcyclopentadienyl,pentamethylcyclopentadienyl, butylcyclopentadienyl,sec-butylcyclopentadienyl, tert-butylmethylcyclopentadienyl,trimethylsilylcyclopentadienyl, indenyl, methylindenyl, dimethylindenyl,ethylindenyl, isopropylindenyl, fluorenyl, methylfluorenyl,dimethylfluorenyl, ethylfluorenyl and isopropylfluorenyl.
 3. Thepreparation method of organic-transition metal hydride according toclaim 1, wherein the M² is one or more elements selected from the groupconsisting of Ti, V and Sc, the a is an integer of 2-4, and the b is aninteger of 2-6.
 4. The preparation method of organic-transition metalhydride according to claim 1, wherein the aprotic polar solvent is oneor more compounds selected from the group consisting of tetrahydrofuran(THF), 1,2-dimethoxyethane (DME), dioxane (DXN), diethylene glycoldimethyl ether (Diglyme), dimethyl formamide (DMF), dimethylsulfoxide(DMSO), dimethylacetamide (DMA), hexamethyl phosphoramide (HMPA) andtheir derivatives.
 5. The preparation method of organic-transition metalhydride according to claim 2, wherein the aprotic polar solvent is oneor more compounds selected from the group consisting of tetrahydrofuran(THF), 1,2-dimethoxyethane (DME), dioxane (DXN), diethylene glycoldimethyl ether (Diglyme), dimethyl formamide (DMF), dimethylsulfoxide(DMSO), dimethylacetamide (DMA), hexamethyl phosphoramide (HMPA) andtheir derivatives.
 6. The preparation method of organic-transition metalhydride according to claim 3, wherein the aprotic polar solvent is oneor more compounds selected from the group consisting of tetrahydrofuran(THF), 1,2-dimethoxyethane (DME), dioxane (DXN), diethylene glycoldimethyl ether (Diglyme), dimethyl formamide (DMF), dimethylsulfoxide(DMSO), dimethylacetamide (DMA), hexamethyl phosphoramide (HMPA) andtheir derivatives.